The goal of the proposed experiments is to discover the mechanism by which the bag-of-marbles (bam) and benign gonial cell neoplasm (bgcn) gene products act to control the earliest steps in female germ cell differentiation from germ line stem cell precursors. Mutations in bam and bgcn have the same phenotype. Loss of function of either gene causes over proliferation of what appear to be primordial germ cells or germ line stem cells in females and over proliferation of interconnected, mitotically amplifying spermatogonia in males. Thus, in both sexes, Bam and Bgcn play a critical role in choices between proliferations as an undifferentiated precursor versus initiation of differentiation. The investigator proposes four aims to explore how Bam and Bgcn function. 1) To determine if the bam and bgcn proteins act together, the investigator will determine if bam and bgcn proteins co-localize in the cell or co-immunoprecipitate. 2) To investigate the mechanism of action of Bgcn and Bam, especially a possible role Bgcn in translational control, the investigator will screen for proteins that interact with Bgcn in the yeast two hybrid system and test if the Bgcn protein binds to RNA (as predicted based on its sequence homology). 3) To explore whether Bam protein function in the fusome is important for regulation of early germ cell differentiation, the investigator will identify the fusome targeting sequences in the Bam protein. If these can be eliminated without destroying Bam activity, it would argue against the investigator's model that localization of Bam protein to the fusome is important for its function in controlling germ cell fate. 4) To identify other components of the mechanism, the investigator will screen for mutations that enhance a weak bam mutant. In addition, the investigator will attempt to identify upstream regulations of bam using a screen for mutations that alter the cell type specific pattern of bam transcription or tiotranslantion.